1. Field of Invention
The invention relates to a control technology for an internal combustion engine mounted in a vehicle.
2. Description of Related Art
An air fuel ratio control (fuel injection control) technology with higher accuracy becomes indispensable for coping with emission regulations that has been becoming increasingly severe year by year. In order to realize the air fuel ratio control with higher accuracy, the accuracy of calculating an amount of air charged in the cylinder, that is, intake air amount within a combustion chamber of an internal combustion engine has to be further improved. Such calculation has been disclosed in the United States Patent Application Publication No. 2002/0107630 A1 in which the amount of air within the cylinder is calculated using an intake system model, for example. The intake system model is intended to clarify the behavior of the intake air that flows from the throttle valve to the intake port of the combustion chamber.
The behavior of the intake air that flows through the intake passage will vary with aging, for example, sediments deposited on the intake passage. Accordingly, the actual behavior of the intake air may not accord with the behavior in the intake system model, resulting in an error in the estimated amount of air within the cylinder. An opening/closing characteristic of a valve provided in the intake port of the combustion chamber will also vary with aging, for example, mechanical wear or deformation of a valve system and the like. This may also cause the error in the estimated amount of air in the cylinder. Such error is caused not only by the aging as aforementioned but also by the piece-to-piece variation among internal combustion engines at a stage immediately after producing thereof.